(define index
  (native_function "
    Proc.new do |arguments, interpreter|
      arg1 = interpreter.evaluate(arguments[0])
      arg2 = interpreter.evaluate(arguments[1])  
      index = []
      i = 0 
      arg1.each do |element|
        if arg2 == element
          index << i 
        end
        i += 1
      end
      if index.length == 1
        index[0]
      else
        index
      end
    end
  "))
